[InvisiBill]

For whatever it's worth, I ran into a lean spot around 6-7k when I put slipons on my EX500. It would actually sputter like I was running out of gas, even though it seemed fine elsewhere in the range and before the exhaust change.

I assumed that was just the leanest spot in the stock setup, and my change had leaned it out enough that it became noticeable. I switched to adjustable Factory Pro needles using the second slot, and it seemed to be a great fix.

One of the forum oldtimers stated that a lean spot there was indicative of the valves needing to be adjusted. However, I had never heard that mentioned previously, in many years of hanging out there, even though he made it sound like common knowledge. This doesn't seem too likely in your case, but it might be worth checking.